The present invention relates to the architecture of a packet switching system having self-routing switches.
As described in xe2x80x9cDigital Switching Systemxe2x80x9d edited by The Institute of Electronics and Communication Engineers of Japan, Mar. 15, 1986, pp. 128-130, a conventional multi-processor type switching system is so constructed as to use the function distribution and the load distribution in combination wherein the switching processing function is divided into a plurality of blocks which are allotted to individual processors. Additional processors of the same function as that of the individual processors are further provided in accordance with the magnitude of the load.
The function distribution faces the following problems:
(1) A fault of, for example, software in one of the processors influences the whole system very greatly.
(2) The interface between processors depends on the method of dividing the function and with loose interface, the process overhead generally tends to increase.
(3) Even the minimum scale of construction of the system has a plurality of processors. In digital switching systems, even when load distribution is adopted in order to let one processor (unit) have completely independent function, such control as path setting with respect to each call is required in the tandem unit adapted to perform connection between units, as the capacity of the system increases.
For the purpose of improving the switching throughput, the self-routing switching system is promising being that it realizes switching processing using a packet of fixed length, as represented by the asynchronous transfer mode (ATM), in terms of hardware. An example of load distribution architecture of an ATM switching system using self-routing switches is disclosed in xe2x80x9cA Study on the Architecture of the ATM Switching Networkxe2x80x9d, Technical Report SSE-38 of The Institute of Electronic Information and Communication Engineers of Japan, Jul. 19, 1989. However, in this example, a module for coupling distributed modules includes a control processing for performing a packet header processing, raising a similar problem to that in function distributions as described above.
In the aforementioned conventional systems a switching unit (tandem unit) adapted to couple switching units for load distribution (local units) must perform control for path setting in respect of each call and the control signal must be terminated so as to carry out part of the switching processing. This leads to problems that reliability of the tandem unit causes a bottleneck in the system and even the minimum construction needs the tandem unit together with the local units.
A first object of the invention is to construct a complete load distributed architecture in a distributed type packet switching system by providing a local unit with a independent call processing switching function and causing a tandem unit to perform only the switching operation by a self-routing switch without effecting any call processing control corresponding to a control signal and including termination of the control signal.
A second object of the invention is to execute the outgoing route control handling resources of the system in the above load distributed architecture without using the common access unit/common memory.
To accomplish the first object, according to one aspect of the invention, a packet switching system is constructed such that an output port of a self-routing switch inside a tandem unit is designated in an originating local unit; a single virtual channel (VC) is set up between originating and destination local units and a virtual channel identifier (VCI) of the VC is determined in the destination local unit; and bandwidth allotment between the local unit and tandem unit is managed by the local unit.
To accomplish the second object, according to another aspect of the invention, a packet switching system is constructed such that a bandwidth allotment condition corresponding to an outgoing route is stored with respect to each local unit; when the bandwidth use condition is changed, all of the other local units are informed of the change; and all of the other local units are periodically informed of the bandwidth use condition.
When a call is originated, a start signal including a circuit bandwidth allotment condition between a call originating local unit and the tandem unit is transferred from the call originating local unit to a destinatior local unit and in the destinations local unit, an optimum route between local units is selected in accordance with the originating circuit bandwidth allotment condition and the circuit bandwidth allotment condition between the destination local unit and the tandem unit. A VCI on that circuit is hunted and a start completion signal including this information is returned to the originating local unit. When receiving the start completion signal, the originating local unit sets, on the basis of the selected route, output ports of individual self-routing switches inside the originating local unit, tandem unit and destination local unit in a label conversion table, and adds this information to a subsequently transferred user information packet.